This invention relates to brushes for applying cosmetic materials and the like, and to methods of making such brushes. In an important specific sense, to which detailed reference will be made herein for purposes of illustration, the invention is directed to twisted-in-wire mascara brushes having thermoplastic fiber bristles.
A twisted-in-wire mascara brush includes an elongated twisted wire core and a multiplicity of bristles clamped at their midpoints in the core and extending radially outwardly therefrom, with free tips cooperatively defining a notional envelope or profile of the brush. The core is constituted of two lengths of wire, which may be initially separate or may be opposed legs of a single U-shaped wire, twisted together into a helix to hold the bristles between them. This core has a proximal end, usually mounted on a stem, and a free distal end to which the array of bristles ordinarily extends; the stem itself typically is carried by and projects from the cap of a mascara container, the cap serving as a handle for manipulation of the brush by a user.
When the cap is seated on the neck of the container, the brush is inserted within the container interior so as to be immersed in the contained mascara. Upon removal of the cap from the neck, the brush is withdrawn from the container, bearing mascara on its bristles, and passes through a wiper mounted in the container neck which controls the amount of mascara carried from the container on the brush. The user, holding the container cap, then manipulates the brush to apply the mascara to, and distribute it over, the lashes. Thus, the brush performs several functions in use: transporting mascara from the container to the lashes, depositing it on the lashes, and combing and arranging the lashes.
Some twisted-in-wire mascara brushes employ straight thermoplastic (e.g. nylon) bristles of solid cylindrical shape and substantially uniform thickness with ends defining a cylindrical or conical (tapering) profile or a profile having a proximal cylindrical section and a distally tapering distal section. The manufacture of these brushes involves initially assembling the bristles and the core wire, twisting the wire to produce an array of radiating bristles gripped in an axially rectilinear core, and then trimming the outer ends of the bristles in the array to achieve the desired profile shape.
Heretofore, however, numerous modifications have been introduced or proposed, especially to enhance the performance of some one or more of the diverse functions listed above. Thus, bristles of various different cross-sections including hollow cylindrical fibers, longitudinally grooved fibers and fibers of multi-lobed cross-section have been used (see, e.g., U.S. Pat. Nos. 4,733,425 and 5,197,497), as well as fibers of irregular cross-section (see, e.g., U.S. Pat. No. 6,016,815). In addition, fibers having different physical characteristics or properties, such as relatively stiff and relatively soft fibers, have been combined in a single brush, either intermixed together throughout the length of the brush (U.S. Pat. No. 4,861,179; see also U.S. Pat. No. 4,964,429) or separately disposed in discrete tandem zones along the brush length (see, e.g., U.S. Pat. Nos. 5,482,059 and 5,709,230), stiffer fibers being preferred for combing lashes and softer fibers being advantageous for transporting and delivering mascara. Again, it has been proposed to trim the bristles into profile shapes more complex than simple cylinders or cones, so as to provide profile edges or faces that aid in combing lashes and distributing mascara therethrough (see, e.g., U.S. Pat. Nos. 4,898,193 and 5,357,987).
The use of thermal energy for selective reduction in length of bristles in a twisted-in-wire mascara brush has been described, for example, in U.S. Pat. Nos. 5,197,497 and 5,345,644, wherein the brush is constituted of bristles of larger section and bristles of smaller section differing from each other in resistance to heat or melting point so that upon exposure to heat, the bristles of lower heat resistance or melting point become shorter than those of higher heat resistance or melting point; the heat treatment also forms bulges at the ends of the bristles owing to melting of the ends. Melting of bristle tips to round them by inserting a twisted-in-wire brush in a heating chamber is described in U.S. Pat. No. 4,998,779, which notes that laser beams have been used to melt and round bristle tips of brushes in which all the bristles are oriented in the same direction, but that such processes are unsatisfactory for twisted-in-wire brushes. U.S. Pat. No. 5,941,605 describes use of a laser beam to cut the bristles of a cosmetic brush so as to produce a desired brush profile, but without melting the bristles being cut.